As shown in FIG. 1, an intravenous (IV) system for delivering an infusion solution into a vein includes: an infusion solution bottle 1, in which the infusion solution is contained; an insertion spike 11 adapted to be inserted through a sealing plug of the infusion solution bottle 1 to allow the infusion solution to be flown out from the infusion solution bottle 1; a drip chamber 12 fixed to the lower end of the insertion spike 11 so that the infusion solution can fall in drops 12a (counted in a unit of gtt) within the drip chamber 12; an injection needle 14 adapted to be inserted into a vein; a tube 13 for interconnecting the drip chamber 12 and the injection needle 14 to serve as an infusion passage for the infusion solution; and an infusion flow regulator 15 mounted in the middle of the tube 13 to be capable of regulating the flow rate of the infusion solution.
In general, the insertion spike 11, the drip chamber 12, the tube 13, the injection needle 14, and the infusion flow regulator 15 are fabricated in one set, wherein the set fabricated in this manner is referred to as an infusion set 10. After the infusion solution in the infusion solution bottle 1 connected to the infusion set 10 is completely infused to the patient, only the empty bottle 1 may be replaced by a new one containing the same infusion solution if it is necessary to continuously inject the infusion solution to the patient. In addition, the insertion spike 11 and the drip chamber 12 are fabricated to make each of the drops 12s of the infusion solution fall within the drip chamber 12 in the form of a water drop with a predetermined volume. For example, if they are fabricated to form 20 drops per 1 cc of the infusion solution, the volume of one drop will be 1/20 cc, and if they are fabricated to form 60 drops per 1 cc, the volume of one drop will be 1/60 cc. Therefore, if the drops' falling interval within the drip chamber 12 is measured, it is possible to calculate the flow rate of the infusion solution injected through the infusion set 10.
For injecting an infusion solution to a patient, the flow rate of the infusion solution is prescribed in consideration of the type of the infusion solution, the kinds of agents mixed in the infusion solution, the condition of the patient, and the kind of the disease of the patient, and the infusion flow regulator 15 is tuned so as to allow the infusion solution to be injected with the prescribed flow rate. Regulating the flow rate of the infusion liquid is very important since a medical accident may occur if the flow rate of the infusion solution being infused is not matched to the prescribed flow rate. Such an infusion flow regulator 15 has a manipulation unit 15a for regulating the cross-sectional area for passage of the infusion liquid through the tube 13, so that the injection flow rate of the infusion liquid can be regulated by manipulating the manipulation unit 15a. 
The infusion flow regulator 15 shown in FIG. 1 is a so-called “roller clamp” type infusion regulator, in which the manipulation unit 15a is formed in a roller type. Referring to the infusion flow regulator 15 in more detail, a tube 13 is inserted through a recess 15b having opened top and bottom ends, and then the roller type manipulation unit 15a adapted to press the tube 13 is guided along an elongated slot 15c upward and downward. Since the depth of the recess 15b is gradually reduced as approaching the lower end of the groove 15b, and hence the tube 13 is pressed more and more as the roller 15a is moved more and more to the lower end of the groove 15b, the injection flow rate of the infusion liquid is regulated by measuring the flow rate at plural points while intermittently moving the manipulation unit 15a, and by stopping the movement of the roller 15a when the flow rate arrives at a desired level.
However, the infusion flow regulator 15 shown in FIG. 1 has a disadvantage in that since the flow rate should be measured while seeing the drip chamber 12 whenever the roller type manipulation unit 15a is stopped at a point, complicated measurements should be repeatedly performed, which will deteriorate the accuracy of flow rate regulation.
FIG. 2 shows an IV flow regulator type infusion flow regulator 15. The IV flow regulator type infusion flow regulator 15 is configured to regulate infusion flow rate by manipulating a manipulation unit 15a, which is adapted to be rotatable like a dial, to be matched to one of marked scales 15d, wherein the marked scales 15d are given marked numerical flow rate values 15e, respectively. As a result, the infusion flow rate can be regulated through a single manipulation of the manipulation unit 15a. More specifically, if the manipulation unit 15a is matched to one of the scales 15d, which is given a numerical flow rate value desired for infusion among the numerical flow rate values 15e, the cross-sectional area of the infusion passage (not shown) is regulated to allow the infusion solution to be infused with the flow rate corresponding to the numerical flow rate value desired for injection. Here, the numerical flow rate values 15e are those determined by hanging an infusion solution bottle up at a designated reference height when fabricating the infusion flow regulator, setting the infusion set 10, and then measuring the flow rate while being injected. As a result, it is possible to regulate the flow rate easily and conveniently by tuning the manipulation unit 15a with reference to the numerical flow rate values 15e after hanging the infusion solution bottle 1 up at the reference height.
However, the flow rate of an infusion solution injected to a patient by an intravenous injection system is determined not only on the basis of the installation height of the infusion solution bottle 1 but also on the basis of various factors, such as the viscosity of the infusion solution, the diameter of the injection needle 14, the venous pressure of the patient, the diameter and material of the tube 13, the ambient temperature, and the atmospheric pressure. Accordingly, there occurs a substantial difference between a flow rate indicated by one selected from the numerical flow rate values 15e marked on the IV flow regulator type infusion flow regulator and the flow rate practically measured in a state in which the manipulation unit 15a is matched to the selected numerical flow rate value. As a result, it is necessary to regulate the flow rate through repeated measurements of the flow rate like the roller clamp type infusion flow regulator even after the manipulation unit 15e is manipulated and accurately matched to the corresponding one of the numerical values 15e. 
A problem herein may occur when a person responsible for regulating the flow rate of an infusion solution in accordance with a prescribed order trusts the flow regulation capability of such an infusion flow regulator after the infusion set is installed despite of the disadvantage of such an infusion flow regulator as described above. In such a case, the person may misjudge that the infusion flow regulator has been tuned to the prescribed flow rate, which may in turn cause a medical accident. On the other hand, the person may confirm that the infusion flow regulator has not been tuned to the prescribed flow rate by measuring the flow rate for the purpose of confirmation after the person manipulated the manipulation unit to match the manipulation unit to one of the numerical flow rate values 15e that corresponds to the prescribed flow rate. In such a case, however, since a required amount of moving the manipulation unit is not known, the person may repeatedly measure flow rate while intermittently moving the manipulation unit little by little, and then may tune the manipulation unit to a measurement point at which the measured flow rate somewhat corresponds to the prescribed flow rate, or to a point guessed among the repeatedly measured plural points. Following this procedure, the person may consider that the flow rate is correctly tuned. In such a case, a problem may occur due to inaccuracy in measuring flow rate in the process of repeatedly measuring the flow rate. Moreover, such inaccurate tuning of the flow rate makes it difficult to correctly determine when the infusion solution contained in the infusion solution bottle is completely consumed. As a result, the infusion set may not be timely separated from the patient at the time when the infusion solution is completely consumed, or the emptied liquid solution bottle may not be replaced by a new one, which may in turn cause a medical accident.
Therefore, such an infusion flow regulator, which is employed as a means for regulating flow rate when an infusion solution is delivered to a patient, should be fabricated to accurately regulate flow rate by reflecting all the various factors, such as the viscosity of the infusion solution, the diameter of the injection needle 14, the venous pressure of a patient, the diameter and material of the tube, the ambient temperature, and the atmosphere pressure at the time of practically using the infusion flow regulator, without relying on incorrect numerical flow rate values which do not conform to a condition at the time of practically using the infusion flow regulator since they were presented according to a specific test condition when fabricating the infusion flow regulator. In addition, the infusion flow regulator should be fabricated to regulate flow rate through a simple manipulation without repeated measurements of flow rate.
Korean Patent No. 10-0706954 discloses an “infusion flow rate measuring device” invented by the inventor of the present application, wherein the infusion velocity measuring device can measure flow rate only if counter input is performed in accordance with a drops' falling interval. In addition, Korean Patent No. 10-0872089 discloses an “infusion assistance device” also invented by the inventor of the present application, wherein the infusion assistance device outputs sounds matching a drops' falling interval to conform to an intended target flow rate so that an infusion flow regulator can be regulated to allow drops to fall in consistence with the sounds. With the devices disclosed in the above-mentioned patents, it is possible to regulate the infusion flow rate with a simple manipulation, and to quickly measure and confirm the flow rate.
The above-mentioned devices invented by the inventor of the present application have been useful in quickly and conveniently regulating infusion flow rate while carrying the devices. However, there is a problem in that the manipulation unit 15a of the infusion flow regulator 15 should be continuously manipulated until the drops' falling interval becomes matched with that of the sounds. As a result, despite of the distinguishable advantages as compared to conventional infusion regulators in terms of quick regulation and accuracy, what is needed is to improve the above-mentioned devices to regulate the flow rate more quickly and correctly. That is, since the initial position of the manipulation unit 15a is a position for stopping the injection of the infusion solution, and the target point of the manipulation unit 15a for injecting the infusion solution with a prescribed flow rate is unknown in terms of position, the manipulation unit 15a should be slowly and intermittently manipulated until it is positioned at the unknown target point in order to tune the infusion flow generator to the desired prescribed flow rate. Moreover, since drops, which fall within the drip chamber 12, fall in an instant, it is necessary to observe drops' falling more than several times so as to confirm whether the current flow rate accurately conforms to the desired flow rate, even if it is estimated that the current flow rate almost arrives at the desired flow rate. Accordingly, what is needed is to make it possible to find a correct position for the manipulation unit 15a through a single confirmation without repeatedly confirming the correct position when it is required to move the manipulation unit 15a and the correct position is unknown.